The present invention relates to a chemically amplified resist, a chemically amplified resist to be formed on a semiconductor substrate for exposure to a KrF excimer laser transmitted through a mask or a reticule and subsequent post-exposure bake (PEB) treatment prior to a development using a developer to form a photo-resist pattern.
The conventional photo-lithography is carried out by using a g-ray having a wavelength of 436 nanometers or an i-ray having a wavelength of 365nanometers as an exposure light. The majority of the conventional resists for the g-ray or the i-ray were positive resists of dissolution inhibitor type, which comprise a novolak resin as a base resin and naphthoquinone-diazide as a photosensitive agent. It was necessary for scaling down of the device to carry out a lithography using excimer lasers having wavelengths of 248 nanometers and 193 nanometers in the ultraviolet. If the conventional resists for the g-ray or the i-ray are used to carry out the lithography using the excimer lasers, then an absorption of the excimer laser into the resist is too large to obtain he desired or required resist pattern. The photosensitivity is also excessively increased.
Thereafter, a chemically amplified resist was conceived which utilizes a sensitizing reaction by an acid catalyst generated by a photoacid generator. This chemically amplified resist has been used and is about to become the major resist for higher sensitivity shorter wavelength lithography or electron beam lithography. This chemically amplified resist includes an acid generator as a photo-sensitizing agent so that exposure of the resist to the light generates an acid and subsequently a catalytic reaction is caused by the PEB-treatment to solubilize an exposed part of the positive resist or insolubilize an exposed part of the negative resist. Those resists are used for the X-ray exposure and the electron beam exposure. Those resists have sufficiently high sensitivity to compensate for insufficient luminance of an X-ray source or an electron beam source.
In Japanese laid-open patent publication No. 4-44045 and Japanese laid-open patent publication No. 5-80516, binary positive resists are proposed which comprise a protective polyhydroxystyrene resin and a photoacid generator. A ternary positive resist was proposed which comprise a protective polyhydroxystyrene resin and a photoacid generator in addition to a protective bis-phenol-A.
In order to improve the resolution of the chemically amplified resist, it is necessary to increase the contrast in solubility of the developer between the exposed and unexposed parts of the resist. In order to increase the solubility contrast, an amount of a protective base of a protective polyhydroxystyrene as a base resin is used so that a resin protectivity is increased to reduce a dissolving rate of the unexposed part of the resist, whereby the solubility contrast is increased for improvement in the resolution of the resist.
The increase in the resin protectivity of the resist raises the following problems. The protective base has a hydrophobicity. An acid is generated by the exposure and then the generated acid disappears in a surface region of the resist film or is deactivated due to neutralization by a base in atmosphere. The deactivation of the acid or disappearance of the acid prevents promotion of the solubilizing reaction in the post-etching backing process The combination of the above two factors results in a formation of a slightly soluble surface layer, for which reason a subsequent development to the resist film forms a resist pattern having an undesired sectioned shape like generally T-shape as illustrated in FIG. 1 which is a across sectional elevation view illustrative of the conventional resist pattern obtained after development and formed over a semiconductor wafer. A resist pattern 702 formed over a semiconductor wafer 701 is generally T-shaped such that the resist pattern decreases in width toward the bottom. Namely, the resist pattern has no vertical walls. This means that the resist pattern having the T-shaped section is deteriorated in resolution, depth of focus and dimensional accuracy.
FIG. 2 is a graph illustrative of variation in dissolving rate of an exposed part of a resist to a developer over an amount of an exposure light. The above problems are often raised with such a resist that a dissolving rate of the exposed part is small and a dissolving rate of the unexposed part is also small.
In Japanese laid-open patent publication No. 4-369211, it was proposed that the PEB-treatment be carried out in an inert gas to prevent deactivation of the acid. In Japanese laid-open patent publication No. 4-221951, it was proposed that the slightly soluble surface layer be removed. In Japanese laid-open patent publication No. 4-204848, it was proposed that a passivation film be applied on a surface of the resist to prevent deactivation of the acid. The third conventional technique has often been used.
The above technique for applying the passivation film on the resist surface is insufficient to prevent the deactivation of the acid. If the acid disappears from the resist surface during a period of the exposure to the PEB-treatment, then this conventional method is incapable of preventing the formation of the slightly soluble surface layer. This formation of the slightly soluble surface layer allows the resist pattern after development to be T-shaped after development.
Particularly when the reduction in scale or dimension of the resist pattern is required, problems with deterioration in shape, resolution, depth of focus and dimensional accuracy due to the slightly soluble surface layer are extremely serious. In order to solve this serious problem, it is essential to improve the material of the resist film.
In the above circumstances, it is required to develop an improved chemically amplified resist free from the above problems.
Accordingly, it is an object of the present invention to provide a novel chemically amplified resist free from the above problems.
It is a further object of the present invention to provide a novel chemically amplified resist which allows a formation of a resist pattern having vertical walls.
It is a still further object of the present invention to provide a novel chemically amplified resist which may be formed into a resist pattern which allows formation of highly integrated semiconductor devices.
It is yet a further object of the present invention to provide a novel chemically amplified resist which allows an improvement in resolution of a resist pattern.
It is a further object of the present invention to provide a novel chemically amplified resist which allows an improvement in depth of focus of a resist pattern.
It is another object of the present invention to provide a novel chemically amplified resist which allows an improvement in dimensional accuracy of a resist pattern.
The first embodiment of the present embodiment of the invention provides a chemically amplified positive resist including at least both a polyhydroxystyrene resin having a protective base which varies in polarity by an acid catalyst and a photoacid generator, wherein the chemically amplified positive resist is admixed with at least a styrene derivative.
The second embodiment of the present invention provides a chemically amplified negative resist at least including a polyhydroxystyrene resin, a photoacid generator and a crosslinking agent which is capable of exihibiting a crosslinking reaction with an acid catalyst, wherein the chemically amplified negative resist is admixed with at least a styrene derivative.
The third embodiment of the present invention provides a chemically amplified resist which is admixed with at least a kind of styrene derivatives.
The fourth embodiment of the present invention provides a resist pattern comprising a chemically amplified resist material which is admixed with at least a kind of styrene derivatives.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.